Noun
ternary form (uncountable)
(music) A style of composition in which one contrasting section of music is written between two similar outer sections.
By 1686 he had definitely established the "Italian overture" form (second edition of Dal male il bene), and had abandoned the ground bass and the binary form air in two stanzas in favour of the ternary form or da capo type of air. Source: Internet
Binary form arias were in two sections (A–B); arias in ternary form (A–B–A) were known as da capo arias (literally 'from the head', i.e. with the opening section repeated, often in a highly decorated manner). Source: Internet
In Western classical music a simple ternary form has a third section that is a recapitulation of the first (ABA). Source: Internet
Lewis (1959), 96 In the early years of the century, arias in the Italian style began to take over in French opera, giving rise eventually to the French genre of ariette, normally in a relatively simple ternary form. Source: Internet